The Visual Cortex and Beyond: Investigating Long-Term Cortical Plasticity Following Monocular Deprivation.

AIM: To characterise short- and long-term plastic changes in cortical and subcortical structures induced by ultra-long (five-day) monocular deprivation (MD), and to assess the extent and regional specificity of structural changes and their reversibility following the restoration of binocular vision.

METHODS

In this single-arm longitudinal study, 21 healthy adults underwent five structural MRI sessions: at baseline, during MD on days 1, 3 and 5, and after a seven-day recovery period (day 12). MD was induced by occluding the right eye with a translucent eye patch for five consecutive days. Grey matter volume (GMV) changes were analysed using voxel-based morphometry (VBM) for whole-brain effects and generalised estimating equations (GEE) to model temporal trajectories in predefined cortical and subcortical regions.

RESULTS

Ultra-long MD induced dynamic GMV changes in primary and higher visual cortices, with exploratory changes also in subcortical and cerebellar structures. VBM showed cumulative volume increases in bilateral occipital cortex, including calcarine, lateral occipital and fusiform regions, and adjacent cerebellar lobules, peaking between days 3 and 5. Region-wise modelling resolved the temporal build-up of these changes across visual, subcortical and sensorimotor regions; after correction for multiple comparisons, a time-dependent effect remained in occipital and ventral occipito-temporal cortex (occipital pole, fusiform and calcarine cortex), converging with the voxel-wise result. Following binocular restoration, an exploratory GMV decrease was observed selectively in the left middle occipital gyrus, while an exploratory increase was observed in the left hippocampus, compatible with persistent plasticity in associative memory networks.

CONCLUSION

Prolonged sensory imbalance via ultra-long MD induces rapid, region-specific and possibly persistent GMV plasticity in the adult brain. These changes follow temporally stratified trajectories across visual, subcortical and integrative systems, consistent with models of homeostatic and hierarchical plasticity. Corrected evidence supports cumulative occipital plasticity during deprivation; whether the exploratory extra-visual and post-recovery changes reflect persistent adaptation requires confirmation. MD-based paradigms thus offer a controlled window on structural plasticity in both healthy individuals and clinical populations.